Products prepared from acrylic rubber compositions possess heat resistance comparable to silicone rubbers and fluororubbers, and oil resistance comparable to fluororubbers, nitrile rubbers, and hydrin rubbers, and are superior to nitrile rubbers, hydrin rubbers, and the like, in oil resistance at high temperatures. Since the products are excellent in heat resistance and oil resistance and are relatively inexpensive, they are used as sealing parts such as O-rings, gaskets, or packings.
Those cross-linked types of acrylic rubber compositions described in Patent Documents 1 and 2, which contain monomers each having a carboxyl group(s) as crosslinking-site monomers, are materials superb in heat resistance and compression set property. However, these compositions are defective in processing characteristics, particularly in roll tackiness upon kneading and tackiness of unvulcanized (uncrosslinked), dough-like material (green stock), and are thus still deficient in processability. Processing steps therefore tend to become complicated, thereby possibly bringing about a factor of increased cost.
Disclosed in Patent Document 3 is an acrylic elastomer composition, which is obtained by combining carbon black, a silica filler, and the like into an acrylic elastomer, and which is used for production of an O-ring, a gasket material, and the like.
However, when reinforcing materials such as carbon black and silica are simply blended, the resulting composition is still considerably high in roll tackiness upon kneading process, and in tacking among unvulcanized (uncrosslinked), dough-like materials in a vulcanizing (crosslinking) step, thereby problematically resulting in a material exhibiting an insufficient processability.    Patent Document 1: WO2007/145337    Patent Document 2: WO2007/145338    Patent Document 3: JP08-3410A